School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe effect of oxygen and carbon dioxide atmospheres on the quality of packaged fresh-cut lettuce( 1999)The present study investigated the potential of using alternative storage atmospheres to maintain microbial and storage quality of fresh-cut lettuce salad mix for longer periods than those currently obtained in air and traditional low oxygen (O2): high carbon dioxide (CO2) modified atmosphere packaging (MAP). The outcome of this research was to assist the freshcut industry through improved shelf life and safe food supply. The effects of modified atmospheres containing air or 100% oxygen at pH 5.0, 6.0 and 7.0, on the growth and survival of two strains of Pseudomonas fluorescens (FSAW 3107 and ATCC 13525) were determined on an agar surface at 5C for 10 days. The aim of this preliminary study was to determine the response of this spoilage organism in a model system where the surfaces of packaged chilled fresh-cut vegetable and MAP conditions were simulated. The results demonstrated the ability of two different strains of Ps. fluorescens to survive and grow in storage atmospheres of up to 100% O2 tested at any of the pH levels, except pH 5.0. The reduction in the pH of the medium to 5.0 was sufficient to inhibit the growth of the bacteria regardless of storage atmospheres. Further studies compared the impact of 100% O2, 80% O2 : 20% CO2, passive MAP and air atmospheres on the microbial growth and storage quality of fresh-cut lettuce mix stored at 5C for 10 days, using four packaging films of differing gas permeabilities. The study also compared and evaluated the suitability of barrier, experimental, and commercial packaging films for using the 80% O2 : 20% CO2 gas mixture. A 100% O2 storage atmosphere maintained with the barrier packaging film inhibited enzymatic browning in lettuce tissue, as determined by visual assessment and colour measurements. On visual examination, the product was still acceptable for consumption after 10 days of storage at 5C, compared to all other film and atmosphere treatments. Polyphenol oxidase activity declined in lettuce stored under 80% O2 : 20% CO2 and passive MAP storage atmospheres, and was the lowest at 100% O2 treatment compared with that of air, and the atmosphere conditions that developed where high permeability experimental films were used. Accumulation of CO2 to levels above 20% in the barrier and commercial packaging films initially flushed with 80% 02 : 20% CO2 gas composition resulted in several disorders in lettuce, such as severe tissue softening and development of off-odours. The same gas mixture used with a high permeability experimental film stabilised at 20.0% O2 and 5.2 % CO2, and the product quality was poorer than in all other treatments except for lettuce stored under air. Fresh-cut lettuce stored in commercial MAP bags had a passively modified atmosphere comprising 0.9% O2 : 17.1% CO2 after 10 days at 5C. The quality of this product was not acceptable after 8 days, due to discolouration of lettuce and off-odours. In conclusion, of the modified atmospheres tested, 100% O2 retained an acceptable visual quality of fresh-cut lettuce salad mix at 5C, without a marked effect on the growth of pseudomonads, Enterobacteriaceae and the total viable count. The choice of film permeability was also demonstrated to be an important factor when using the alternative storage atmospheres. Film permeabilities that would allow development of storage atmospheres containing CO2 above 20% with high oxygen levels, should not be used since this was shown to promote physiological damage of the fresh-cut lettuce.
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ItemResponses of young sheep to supplements when fed low quality roughages( 1999)The morphological components of which cereal straw is composed vary in composition and nutritive value. In a survey of relevant literature, stem materials (ST) are usually found to be consumed by ruminant animals at a slower rate than leaf material (LF) from the same crop residues when these are fed alone as separated fractions. This is attributed to the higher content of cell wall constituents (CWCs) and often lower content of N of ST. Because ST and LF can vary in proportions in the roughage fed as a basal feed, the response of animals to supplements might also be expected to be variable particularly when the basal feed is offered in excess that permits selection. In particular the response to supplemental N sources varying in ruminai degradability may vary. The objective of this thesis program was to investigate the interactions between the basal roughage and supplement measured as effects on digestion and LW responses of young sheep. The overall hypothesis was that across diets made up of different proportions of LF and ST fractions of cereal straw, the response to N supplements is dependent on CWCs concentration. The program was completed through a series of experiments conducted at the Mt Derrimut Field Satation of the University of Melbourne. In all experiments the animals were fed on a basal feed of LF or ST fractions of barley straw, with supplements including (a) Bar+USS, barley grain (Bar) fortified with urea solution prepared at a ratio of 5:1 (urea plus Na,SO4). (b) USS, urea solution alone added to the basal roughage and (c) FM, fishmeal. With each basal feed one group of lambs did not receive any supplement and served as a control group (CONT). Experiment 1 (Chapter 3) was conducted to evaluate chemical and nutritional characteristics of straw fractions of Parwon cultivar barley. Straw was separated into 4 fractions - stem (ST), leaf blade (LB), leaf sheath (LS) and broken fractions plus weeds (OT). The separated fractions were analysed chemically ( van Soest, 1974) and in vitro digestibility (Tilley and Terry 1964 ) determined. ST was the largest fraction and contained a significantly higher concentration of neutral detergent fibre (NDF; p<0.01) than LB, LS and OT (83.1, 78.6, 76.8,and 71.5 g/100g respectively). ST contained less hemicellulose (HC) than LB but more than LS and OT (37.5, 39.6, 36.3, and 35.7 respectively). N content was lower in ST than in LB, LS and OT fractions (0.4, 0.9, 0.6, and 0.7 respectively). Digestibility in vitro was significantly lower (P<0.001) for ST than for other fractions (38.5, 72.7, 60.1, and 63.0 respectively) while energy required for grinding (Chenost 1966) was much higher (P<0.001) for ST than for other fractions (121, 54.6, 64.2, 56.6 respectivly). In Experiment 2 (Chapter 4) ST and LF fractions of the same Parwon barley straw were fed as the basal feed to lambs and DM intake of ST was 15% lower than for LF (403 vs 473 g/d). When LF feed was supplemented with USS and FM, DM intake was greater by 28% and 25% respectively, while supplementation with Bar+USS resulted in 10% lower LF intake. In contrast, with animals fed ST as the basal roughage, only FM led to an increase in DM intake of only 10%. Supplementation with Bar+US and USS and FM improved overall digestibility, estimated metabolisable energy intake and N intake. Low N intakes on the basal roughages supported low ruminai ammonia-N concentrations (mg/1) immediately before feeding (ST, 20.4 ; LF 35.8), but these were improved where supplements had been fed with each of ST Bar+USS, 263.7; USS, 186.7; and FM, 151) and LF (Bar+USS, 219.5; USS, 62.5; and FM, 150). Six hours after feeding, ammonia-N concentrations (mg/l)were higher for ST (99) still low for LF(35) when fed alone, reduced below the prefeeding levels by supplements of Bar+USS (ST,167; LF 173) but raised by USS (ST, 201; LF 148) and FM (ST, 114; LF, 192). The concentrations of total volatile fatty acids (VFA) in rumen fluid (mMoUl) were not significantly different for ST and LF before feeding except where FM was the supplement, or six hours after feeding except where Bar+USS or USS were fed with LF (before feeding: ST, 51; Bar+USS, 55.7; USS,46.5; FM, 56 ; LF, 42.6; Bar+USS, 53; USS, 55.5; FM, 63.6; 6h after feeding ST, 55.5; Bar+USS, 70.2; USS, 62.1; FM, 50.4 ; LF, 55.7; Bar+USS, 69.5; USS, 60.9; FM, 60.9). Lambs on ST and LF alone lost weight (ST, -105; LF -98 g/d ). Rate of liveweight loss was less when Bar+USS (ST, -32.3; LF -2.4g/d) and USS (ST, -79.8; LF -31.2 g/d) supplements were fed, while FM promoted LW gain (ST, 37.5; LF, 72.4g/d). N retention data was consistent with these LW gains, except where Bar+USS was the supplement, in which case the animals were in positive N balance though losing weight. Wool growth was significantly improved (P<0.001) only by FM on both ST (+47%) and LF (+57%) basal roughages. In Experiments 3 and 4 (Chapter . 5 and 6) the objective was to investigate the factors responsible for low feed intake and poor performance of lambs fed ST compred to those on LF. The DMI (g/d) of lambs fed ST and LF were similar to those achieved in experiment 2; and were significantly greater for LF (P<0.001). Likewise supplements of Bar+USS, USS and FM had similar effects to those reported for experiment 2_ Changes in DMI, MEI ruminai environment before feeding or 6 and:12 hours after feeding were consistent with those recorded during experiment 2. However concentration of total VFA was significantly elevated at 12 hours after feeding. Differences in ruminal environment were evident in terms of VFA concentrations and the distribution of rumen digesta particulate material in different size fractions; both variables were affected both by the basal diet and the supplement. For LF, the proportions of particles >2mm and of very fine particles (0.125 mm) were greater and for particles between 0.5 and 1 mm less those for ST in all cases. Further, the proportion of particles >2mm was less where FM was fed than for any other feeding regime. The mean retention times of rumen fluid, measured from CoEDTA dilution rate, and calculated for rumen particulate material was longer (24%, P<0.01) for ST than for LF but there was no significant effect of supplement on this (Experiment 4, Chapter 6). The mean percentage of very fine particles in the faeces of lambs fed on LF was higher than for lambs fed ST alone or with supplements. Rate of ruminai degradation of OM of ST and LF as measured by nylon bag technique ( Experiment 3, Chapter 5) was similar at 12 and 24 hours but greater for LF than for ST at 48 and 96 hours of incubation. Bar (cracked whole grain) was degraded more rapidly and extensiveley than FM; in LF fed sheep this difference was more marked. Rate of degradation of acid detergent fibre (ADF) was influenced by the kind of supplement and was greatest in lambs given FM , and least in lambs given ST with no supplement. Only the FM supplement resulted in LW gains, though rates of LW loss were least and LW gains with FM were greatest with LF as the basal roughage. The responses are interpreted as flowing from the greater proportion of ADF and lignin in the CWCs content and the greater digestibility of ADF in the LF fraction. The ST feed fraction with higher concentrations of cell wall constituents (CWCs) as NDF was eaten at a slower rate (Experiment 5, Chapter 7) and digesta particulate material and, in these experiments, the fluid phase are retained longer in the rumen. LF showed not only an advantage over ST in these respects but also in terms of a number of important digestion parameters supported a greater response to supplements, particularly N supplements of low degradability. Thus FM is these experiments interacted with the roughage component of the diet. It provided more consistent ruminai ammonia concentrations supporting a better environment for microbial activity and growth. Microbial protein together with undegraded dietary protein together provide a balance of nutrients that allows LW gains on otherwise submaintenance basal feeds. The greater enhancement of performance with LF compared to ST and the particle size measurements suggest that greater fragmentability of LF may be a major contributor . In terms of technical improvement of livestock feeding systems, providing the animal with opportunity for selection of more leaf and less stem may improve the likelihood of responses to supplements but this was not demonstrated in Experiment 5. FM was used as the experimental supplement to provide slowly degraded and undegraded dietary protein of high biological value to the animal. FM is expensive and other crop byproducts and local feed materials with properties of slow degradability of protein and good amino acid balance need to be identified. An alternative strategy would be to provide a maximum opportunity for the selection of most digestible parts. If refusals are then collected, quality could be further improved with alkali treatment and necessary supplementation. This would provide a strategy for the use of morphological fractions which could be an economical approach for the efficient utilization of roughages.
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ItemSeed dormancy in vetch (Vicia species)( 1999)The aims of this study were to develop appropriate methods for screening Vicia species for dormancy and dormancy mechanisms and determine factors responsible for the development of seed impermeability and how impermeability can be overcome. The materials recommended by the International Seed Testing Association (ISTA 1993 and 1996) for the germination of seeds were evaluated. Loamy sand, paper towel and Petri dishes were all suitable for germination of Vicia seeds. The three types of material have their advantages and disadvantages but the advantages outweighed the disadvantages in the different type of media. The towel method was chosen for this study because it was easier to germinate many seeds (100 seeds per towel) at a time and the towels could be reused until the end of the study. Also, there was no need for regular watering during the tests because towels held enough water for two weeks. The optimum temperature for Vicia seed germination was identified to be between constant 15 and 20C. These results agree with recommendations by ISTA of germinating most Vicia seeds at 20C. A fluctuating temperature of 22/11C also had good germination but the germination rate was reduced. Ten Vicia species and subspecies were assessed for dormancy. Vicia sativa, V. benghalensis, V. ervilia and V. articulata had no impermeable seeds. Almost all the V. villosa accessions had a high level of impermeable seeds ranging from as low as 10% to a high of 60%. Breeding against this trait has been successfully achieved by SEEDCO, a seed company based in South Australia and cultivars with reduced levels of impermeable seeds have been released. The remaining species; V. sativa ssp nigra, V. sativa ssp sativa, V. serratifolia, V. amphicarpa and V. lutea all had higher levels of impermeable seeds ranging from 50 to 95%. These studies concentrated on overcoming impermeable seed coat by mechanical and chemical scarification. Scratching the seed coat with a pin was enough to enhance germination. Commercial scarifier was not as effective as scratching the seed coat with a pin. This could partly explain the need to penetrate the seed coat as achieved by a pin as compared to rubbing off part of the seed coat with sand-paper. The use of sulphuric acid was effective in enhancing germination in Vicia seeds with high proportion of impermeable seeds. Exposure of the seeds to the acid for 30 minutes was effective. Low temperature storage (5C) reduced the level of impermeable seeds in most species. The seed moisture was increased under low temperature storage and this resulted in higher germination. This type of storage is not suitable for long term storage but can be used if the relative humidity is reduced to about 0%. High temperature storage reduced seed moisture and encouraged seed impermeability. Fluctuating temperature of 22/11C reduced the proportion of impermeable seeds. Storage environment also played an important role in the development of impermeable seeds in Vicia. Dry conditions imitated by desiccator reduced seed moisture and resulted in higher levels of impermeable seeds. Seed storage under laboratory conditions had no effect on the proportion of impermeable seed.
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ItemChemical treatment of wood and its effect on wood/water interactions( 1999)Wood-water interactions including the effect of grain orientation, sample size and water potential in Pinus radiata D.Don were investigated. The influence of various chemical treatments on the wood-water interaction was also evaluated. The uptake of moisture by wood soaking in water was determined using the water soak method developed by Rowell and Banks (1985). Treatments with surfactants such as ammoniacal copper-didecyldimethylammonium chloride (DDAC-ACQ) and linoleate salts increased the initial uptake rates of the wafers, whilst treatment with copper chrome arsenic (CCA), linseed oil (LO) and a combined CCA/LO treatment reduced uptakes of moisture. The length of time used to assess the water repellent effectiveness (WRE) was found to be crucial to the test, with most of the reduction in WRE occurring in the first 15 minutes of soaking. Exposure of wax treated wafers to weathering indicated an initial gradual reduction in efficacy, which decreased more rapidly as the length of exposure time increased Tests on the effectiveness of different wood coatings subjected to high humidity illustrated the importance of a film with low permeability and some elasticity. Wood blocks coated with resorcinol-formaldehyde resin initially inhibited moisture ingress, but failed after prolonged exposure. An extra coat increased the time required before failure. Coating the wood wafer with a silicone resin slightly reduced the uptake of water into the wafer. However, this resin was more permeable than the resorcinol-formaldehyde resin and was not as efficacious. The effect of various oil treatments on the uptake of water vapour indicated that the distribution of the oil is critical to inhibiting vapour uptake. No significant difference was found between the moisture uptake of hardwood and softwood stakes. Treatment with trimethylborate (TMB), DDAC-ACQ and CCA had no significant effect on the extent of vapour taken up by the wood. An experiment designed to investigate the importance of sample size when assessing wood performance was carried out using matched samples of treated and untreated quartersawn and flatsawn Pines radiata D.Don. It was found that samples treated with DDAC-ACQ and exposed outdoors experienced a greater flux in moisture content compared to controls. CCA reduced the extent of moisture uptake, with the incorporation of oil further enhancing the short term weathering performance. Quartersawn wood exhibited a smaller moisture flux than the flatsawn timber.However, the performance of CCA/Oil treated quartersawn wood was only marginally better than the quartersawn controls. Laboratory trials gave an identical treatment ranking as the exterior trial; however the use of the smaller sample size was identified as being inappropriate for the assessment of check formation in the timber. A sample size effect was demonstrated when assessing the efficacy of treatments by the water soak method. A treatment gradient could be demonstrated when whole stakes were impregnated with CCA and linseed oil by a two-stage process. The test indicated that the significance of improvements in the water repellency of treated wafers diminishes when larger sized samples are investigated. The effect of soil water availability on wood moisture content was determined for untreated hardwood and softwood sticks. At low soil moisture contents, hardwood sticks were found to be significantly more saturated than their softwood counterparts. At higher soil water contents (100% water holding capacity (WHC)) the performance of the two species of wood became less significant. Chemical treatment was found to have a significant effect on reducing wood moisture levels when free water was available in the soil. Linseed oil was responsible for a significant reduction in moisture uptake, by blocking the pathways for water uptake as well as by decreasing the void volume available in the wood for water to occupy. Incorporation of a drying agent did not improve the quality of the film formed by the linseed oil as no significant change in water repellent performance was identified. The uptake and movement of water through a horticultural post was simulated using a procedure described by Baines and Levy (1979). The wick action of heartwood and sapwood stakes of Pinus radiata D.Don was investigated with distinct moisture distribution and behaviours found. Heartwood, being less permeable, showed a reduction in the volume of vapour that moved through the wood, as well as a much lower stake moisture content compared to the sapwood. This difference was most pronounced above the air/water interface and helps to explain the difference in decay resistance exhibited by the two wood types. End sealing the stakes with silicone resin was found to have no significant effect on the wick action of the stake. Lumen filling treatments with wax, oil and alkyd resins were found to significantly alter the wick action of the stakes. Treatment with low concentrations of surface active compounds such as DDAC-ACQ and linoleate soaps were found to increase the rate of water uptake. At higher concentrations the presence of the surfactant increased the hydrophobicity of the wood and reduced moisture uptake. Biological testing using a fungal cellar determined that treatment of the wood with CCA/LO, CCA, DDAC-ACQ/LO, LO and DDAC-ACQ significantly improved the resistance of the wood to decay. The incorporation of linseed oil did not cause a significant improvement to the decay resistance of the stakes over the trial period
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ItemChlorophyll fluorescence for rapid assessment of salt tolerance in eucalypts( 1999)Chlorophyll fluorescence parameters were investigated, using the OPTISCIENCES 0S5-FL fluorometer. for their potential as non-invasive rapid indices of salt stress in Eucalypts. Cloned E. camaldulensis and E. urophvlla x grandis plants were subjected to salinity (0-650mM NaCI) and chlorophyll fluorescence parameters measured. Dark-adapted and quenching parameters did not show consistent responses to salinity stress. The light-adapted parameter Fds, measured by the Yield program, showed a predictable trend in response to salinity treatment. Measurements were influenced by diurnal changes, positional effects and environmental changes. It is therefore important to measure Fd, within a controlled environment, randomising and rearranging plants during the course of the experiment. Fully expanded, green, attached leaves should be used for measurement and salt concentration should be raised slowly (e.g. 50mM/5 days) after a concentration of 300mM NaCI has been reached. Statistical analysis should be performed using non-parametric methods as chlorophyll fluorescence parameters are not normally distributed. In most cases Fds declines before the onset of visible physical symptoms, however it is affected by sudden shock. It is therefore important that results show a consistent decline in Fds and/or Fds decreases markedly (e.g. 40-50% of the control). This method allows for the objective ranking for salt tolerance of both seedlings and clones. Fds may also have the potential to detect individual responses to salinity and assist the detection of individuals with uncharacteristic responses or unsatisfactory root systems within clones.
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